Steam cooled nuclear reactor



Filed Nov. 18. 1960 FIG. IA.-

United States Patent Ofl Fice 3,183,167 Patented May 11, 1965 3,183,167STEAM CODLED NUCLEAR REACTOR Norman Bradley, Culeheth, Warrington,England,

assignor to United Kingdom Atomic Energy Authority, London, EnglandFiled Nov. 18, 1960, Ser. No. 70,251 Claims priority, application GreatBritain, Nov. 26, 1959, 40,172/59 3 Claims. (Cl. 176-59) This inventionrelates to nuclear reactors of this kind comprising a moderatorstructure penetrated by a lattice of blind-ended channels orientatedvertically with their blind ends lowermost, with nuclear fuel elementsin the channels and with coolant flow barrier sleeves disposedlengthwise in the channels between the channel walls and the fuelelements to define outer, inflow paths with the channel walls and inner,outflow paths with the fuel elements. Such reactors are hereinafterreferred to as of the kind described.

When the coolant employed for such nuclear reactors is steam, problemarise in the removal of collected condensate from the lower ends of thechannels, the condensate being formed by contact of inflowing steam withthe cooler walls of the channels.

According to the invention a steam cooled reactor of the kind describedis characterised in that each channel has beneath the lower end of itsbarrier sleeve a battle which is so disposed with slight clearance fromthe channcl walls to allow steam condensate to descend on the walls ofthe channel past the battle and which is shaped to deflect steam coolantflowing down through the outer, inflow path to flow in counter-directionup through the inner, outflow path, means being provided for removingcondensate collected below the baifle.

The invention provides a covering for collected condensate so thatentrainment with outflowing steam is prevented. When little or nocondensate has collected (for example, upon start-up" of the reactor)the invention L prevents the condensate removal lines from beingsubjected to the full force of inflowing steam.

An embodiment of the invention will now be described by way of examplewith reference to the accompanyin g drawings wherein:

FIGURES 1A and 1B respectively combine to provide a side view in medialsection.

Referring to the figures, a steam-cooled, heavy Water moderated nuclearreactor has a moderator-containing tank-like structure 2 provided with alattice of vertically orientated fuel element channels 3 of blind-endedform and having internal coolant flow barrier sleeves 4 to accommodatefuel elements 5 and to define inner, outflow and outer, inflow paths 6and 7 respectively. Dished baffles 8 are provided below the ends of eachof the barrier sleeves 4, the baffles extending transversely across thebottom of the channels 3 with slight clearance 9 from the channel walls.Condensate is removed from the lower ends of the channels 3 by outlets10 below the bafllcs 8.

The moderator tank 2 is pierced by a lattice of calandria tubes 11 whichlocate the channels 3, the tank 2 being divided by division plates intothree horizontal sections 12, 13 and 14 respectively. Section 14contains light Water (H O) for neutron shielding and section 13 theheavy water (D 0) moderator whilst section 12 contains a structure ofgraphite granules 70 and boron steel plates 71 for neutron shielding,although it could contain a combination of graphite and light water.

The steam coolant is conducted to and from the channels 3 by pipes 16connected to the channels 3 by demountable joints 17. The pipes 16 havecoolant inlets and outlets 18 and 19 respectively, divided from eachother by scaling rings 20 carried on the upper ends of the barriersleeves 4 which extend into the pipes 16. The pipes 16 terminate at acharge face 21 and are pressuresealed by removable plugs 22.

The barrier sleeves 4 are located within the channels 3 and pipes 16 byspiders 23 and support in turn the fuel elements 5 which are carried insleeves 24 having lugs 25 attached to their upper ends. The lugs 25 restupon support rings 26 attached to the inner walls of the barrier sleeves4.

The sleeves 24 carrying the fuel elements 5 extend to the lower ends ofthe barrier sleeves 4, spaces 27 between the sleeves 4 and 24 providingthermal insulation to discourage the transfer of heat by conduction fromthe fuel elements 5 to the channels 3.

The upper ends of the sleeves 24 support removable neutron scatter plugs28, which, whilst allowing a tortuous but unrestricted flow path tocoolant, prevent the passage of neutrons along with the coolant byscattering and absorption. A full description of a neutron scatter plugis disclosed in my co-pending US. application Serial No. 834,198, filedAug. 17, 1959, and now Patent No. 3,132,998, granted May 12, 1964-. Theneutron plugs 28 may be raised and lowered by lifting studs 29 attachedthereto. Similar studs 30 are attached to spiders 31 carried in theupper ends of the sleeves 24.

The channels 3 are of. zirconium and the pipes 16 of steel. As theco-eiflcient of expansion of zirconium is less than that of steel, thedemountable joints 17 are designed accordingly. The joints 17 includeflanged ends 32, 33 on pipes 16 and channels 3 respectively, clampedtogether by high-tensile steel studs 34 and nuts 35. The flanged end 32of each steel pipe 16 has an annular ring 36 integral with the end 32and mating with a face 37 on the end 33 of each zirconium channel 3.When the reactor is in operation and the joints 17 subjected to hightemperatures, the annular rings 36 of the flanged ends 32 yield byplastic deformation to allow differential expansion of the channels 3and pipes 1s whilst maintaining a leak-tight seal.

Stressing of the joints 17 by bending moments created by horizontalmovement of the inlets and outlets 18, 19 of the pipes 16 are relievedby guide members 33 which allow lengthwise movement only of the pipes 16and channels 3. This arrangement is disclosed more fully in myco-pending US. application Serial No. 848,722, filed Oct. 26, 1959. Theguide members 38 include fixed parts 39 and movable parts 46. The fixedparts 39 have lower flanges 41 rigidly secured to the top of themoderator tank 2 by bolts 42 and have external splines 43 for slidingengagement with internal splines 44 of the movable parts 46. The upperends of the movable parts 46 embrace the pipes 16 and are weldedthereto. Recesses 45 formed within the movable parts are closed byplates 4d, 47 welded to pipes 16 and movable part 40 respectively. Therecesses are filled with a mixture of graphite granules 61 and boronsteel plates 62 so that the close-packed guide members 38 provide aneutron shield above the moderator tank 2. The movable parts 40 aresealed to the upper face of a heat-insulating slab 43 covering the topof the moderator tank 2 by bellows 49 mounted on seal-plates 50. Thebellows 49 have apertures 51 connected to a common take-off pipe 52communicating with a sensing device so that out-leakage of reactorcoolant may be readily detected.

The channels 3 have lower ends 53 with apertures 54 to accommodate thecondensate outlet pipes 10 which are connected to external drain trapsof conventional type (not shown). The outlet pipes 10 are of steel andhave s "es boiled to the zirconium channel ends 53 go tensilesteel bolts56. The flanges 55 have annular rings 57 integral with the flangesmating with faces 58 on the channel ends 53 to provide joints similar tothe joints 17 connecting the upper ends of the channels 3 to the pipes16. The flanges 55 also carry plates 59 which support the baiiles 8. Thebaffles have central drain holes 60.

The lower ends of the calandria tubes 11 are closed by neutron shieldplugs 63 having flanges 64 secured to the bottom of the moderator tank 2by bolts 65, the tank 2 being provided with steel plates 66 forshielding purposes. The plugs 63 have apertures 67 to accommodate thecondensate outlet pipes 10.

Spaces 68 between the calandria tubes 11 and channels 3 provide thermalinsulation to discourage the transfer of heat by conduction from thechannels 3 to the calandria tubes 11 and hence to the moderatorcontained in the tank 2.

When the reactor is in operation, any condensate deposited by theinflowing steam coolant passing down through the outer flow paths 7between the channels 3 and the barrier sleeves 4 will be deposited uponthe walls of the relatively cool channels 3. The slight clearance 9between the batlles 8 and the walls of the channels 3 allows thecondensate to descend between the edge of the baifies 8 and the walls ofthe channels 3 where it builds up in level until it spills over into themouths of the outlets 10. The latter are covered by the baffles 3 whichredirect the steam flow in an upward direction towards the inner flowpath 6. This covering is of particular advantage upon start-up of thereactor when little or no condensate has collected and the condensateoutlets 10 would otherwise be subjected to the full force of inflowin gsteam.

Condensate formed upon shut-down of the reactor and tending to collectin the spaces defined by the upper faces of the batlles 8 in drained offas it collects by way of the drain holes 60 to prevent entrainment withthe steam coolant upon the next start-up.

I claim:

1. In a steam cooled nuclear reactor having a moderator structuredefining a lattice of vertically extending blind-end channels with theirblind ends lowermost; the combination comprising flow barrier tubesrespectively disposed lengthwise in the channels and terminating shortof said blind ends, said barrier tubes defining outer inflow paths andinner outflow paths for the steam coolant, nuclear fuel elements in saidinner outfiow paths, a battle member disposed beneath each of saidbarrier tubes and traversing the greater part of the span of thechannels to define condensate collecting chambers with the lower ends ofthe channels, the periphery of each of said bafile members being clearat least in part from the inner walls of the respective one of saidchannels for the passage of steam condensate from above the said bafflemembers to said chambers and said battle members shaped to constrainsteam coolant flowing down through the said outer inflow paths to flowin counter-direction up through the said inner outflow paths, and meansin respect of each of said channels for removing steam condensatecollected in the respective one of said chambers.

2. In a steam cooled nuclear reactor having a moderator structuredefining a lattice of vertically extending blind-end channels with theirblind ends lowermost; the combination comprising flow barrier tubesrespectively disposed lengthwise in the channels and terminating shortof said blind ends, said barrier tubes defining outer inflow paths andinner outflow paths for the steam coolant, nuclear fuel elements in saidinner outflow paths, a bafile member disposed beneath each of saidbarrier tubes and traversing the greater part of the span of thechannels to define condensate collecting chambers with the lower ends ofthe channels, the periphery of each of said battle members being clearat least in part from the inner walls of the respective one of saidchannels for the passage of steam condensate from above the said battlemembers to the said chambers, and said baifle members presenting agenerally concave face towards impinging steam coolant flowingdownwardly through said outer inflow paths such that said steam coolantis deflected in counter direction up through said inner outflow pathsand means in respect of each of said channels for removing steamcondensate collected in the respective one of said chambers.

3. In a steam cooled nuclear reactor as claimed in claim 2, meansdefining a condensate drain aperture penetrating the centre of each ofsaid baffle members.

References Cited by the Examiner UNITED STATES PATENTS 60,470 12/66Bristol 122-489 623,554 4/99 McAllister et al 122-489 X 1,748,067 2/30Howley 122-489 2,999,059 9/61 Treshow 176-42 3,053,746 9/62 Challenderet al. 176-27 OTHER REFERENCES Yvon: Proceedings of the InternalConference on the Peaceful Uses of Atomic Energy, 1955, vol. 2, page345.

Nuclear Power, September 1957; Coolant Choice for the V.H.T. Reactor,Peter Fortescue; pp. 381-385.

CARL D. QUARFORTH, Primary Examiner.

REUBEN EPSTEIN, Examiner.

1. IN A STEAM COOLED NUCLEAR REACTOR HAVING A MODERATOR STRUCTUREDEFINING A LATTICE OF VERTICALLY EXTENDING BLIND-END CHANNELS WITH THEIRBLIND ENDS LOWERMOST; THE COMBINATION COMPRISING NOW BARRIER TUBESRESPECTIVELY DISPOSED LENGTHWISE IN THE CHANNELS AND TERMINATING SHORTOF SAID BLIND ENDS, SAID BARRIER TUBES DEFINING OUTER INFLOW PATHS ANDINNER OUTFLOW PATHS FOR THE STEAM COOLANT, NUCLEAR FUEL ELEMENTS IN SAIDINNER OUTFLOW PATHS, A BAFFLE MEMBER DISPOSED BENEATH EACH OF SAIDBARRIER TUBES AND TRAVERSING THE GREATER PART OF THE SPAN OF THECHANNELS TO DEFINE CONDENSATE COLLECTING CHAMBERS WITH THE LOWER ENDS OFTHE CHANNELS, THE PERIPHERY OF EACH OF SAID BAFFLE MEMBERS BEING CLEARAT LEAST IN PART FRM THE INNER WALLS OF THE RESPECTIVE ONE OF SAIDCHANNELS FOR THE PASSAGE OF